Thus far, a NOx purifying catalyst has been researched that can effectively decrease NOx (nitrogen oxide) in the exhaust gas of an automobile or the like. Above all, decreasing NOx along with PM (particulate matter) has been an important issue in diesel vehicles.
In diesel vehicles, typically, an oxidation catalyst (DOC) and a diesel particulate filter (DPF) have been arranged in the exhaust path of the diesel engine. However, in the case of further decreasing NOx being demanded in the future, a simple combination of the conventional DOC/DPF will not be sufficient.
Thus, as a method to further decrease NOx in exhaust gas, for example, an exhaust gas purifying apparatus of an internal combustion engine has been disclosed in Patent Document 1 detailed below that is configured so as to use a NOx absorbent that absorbs NOx when the air/fuel ratio of the exhaust gas is lean and releases the NOx thus absorbed if the oxygen concentration in the exhaust gas drops, and the NOx absorbed when the exhaust gas is lean is released from the NOx absorbent when the oxygen concentration in the exhaust gas has dropped.    Patent Document 1: Japanese Patent Publication No. 2600492